Note Number: AG0184
Published: June 2000
Updated: February 2010
The egg of the two-spotted mite, Tetranychus urticae, is minute, globular and an almost transparent pale yellowish-white.
The larva that hatches from the egg has six legs, is pale yellowish-white, minute and oval. The larva moults to become an eight-legged nymph, which becomes the mature mite after two further moults. The adult female is about 0.5 mm long, the adult male about 0.3 mm long. In the summer feeding stage the adult females are a yellowish-green, with two pronounced dark spots, one on either side of the body. In males these spots are less conspicuous. Both sexes possess two reddish eyespots. Only adult females overwinter, after changing to the orange-red, non-feeding stage.
Both nymphs and adults damage plant foliage by piercing the cells and sucking the contents, causing collapse and death of the cells.
The mite is a profuse web-spinner in its active stages. Infested leaves become pallid and may become bronzed and shrivelled. The mites are particularly damaging in hot, dry weather when a life cycle may be completed in just over a week. Plants near dust sources such as dirt roads are particularly susceptible to mite attack.
Two-spotted mites attack a wide variety of plants including peaches, apples, cherries, pears, plums, berries, ornamentals and many vegetables.
The development of the overwintering or hibernating form is initiated by shortened daylength, decreased temperatures and unfavourable food supply. Overwintering females stop feeding and egg-laying, become orange-red and move to shelters on the ground and in cracks in the bark of lower regions of trees (Figure 1).
Overwintering is terminated by the increased temperatures in spring. The mites leave their overwintering sites and lose their red colour as they start to feed. Mites living in protected environments, such as glasshouses, do not hibernate overwinter but continue to feed and reproduce. The females lay up to six eggs a day and usually lay a total of 70 or more. Hatching occurs 3-10 days later, depending on the temperature. Males develop from unfertilised eggs whereas females develop from fertilised eggs. The young mites mature in 4-12 days, depending on temperature, and may live for another three weeks or more. In hot weather the complete life-cycle may be as short as two weeks, and all stages may be found at the one time.
There are two problems in controlling two-spotted mite. The use of broad-spectrum insecticides greatly reduces the number and effectiveness of beneficial insects, and mite populations have developed varying degrees of resistance to several miticides. If chemical control is required, careful selection of a miticide is important. There are several effective miticides available but they may be phytotoxic to some plants. Two-spotted mite has been successfully controlled in Victorian apple and peach orchards by the use of an integrated approach in which chemicals are used in conjunction with the introduced predatory mite Typhlodromus occidentalis.
Presently,T. occidentalis is available commercially in Australia. Overseas the predatory mitePhytoseiulus persimilisis used in glasshouses to control two-spotted mite. P. persimilisis also available commercially in Australia. The predatory mites are susceptible to different pesticides and growers are advised to obtain a list of pesticides toxic to the predators. Such lists are available from the suppliers of the predators. Further information on availability of biocontrol agents can be obtained from the Association of Beneficial Arthropod Producers.Contact/Services available from DEPI
For effective pest and disease control, correct diagnosis is essential.
A commercial diagnostic service is available at the DEPI Tatura. For further information, contact the Diagnostic Service. ph: (03) 9210 9222.
Contact the Customer Service Centre of the Department of Primary Industries, Victoria at 136 186.
For information relating to the safe and appropriate use of chemicals, including management of chemical residues and licensing requirements, call the DEPI Customer Service Centre of 138 186 and ask to speak to your local chemical standards officer or visit www.agriculture.vic.gov.au/chemicalstandards.
This Agnote was developed by David Williams, Biosciences Research Division in June 2000.
It was reviewed by Harold Adem, Farm Services in February 2010.
Published and Authorised by:
Department of Environment and Primary Industries
1 Spring Street
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